In the field of semiconductor manufacturing, it is well known that a pattern can be formed in a surface of a solid substrate by utilizing conventional photolithographic techniques. Conventional photolithographic processes include the steps of providing a photoresist or mask to predetermined areas of a solid substrate, patterning said photoresist or mask, etching the exposed areas of the solid substrate and stripping of the photoresist or mask. In such prior art processes, etching of the solid substrate is generally achieved by employing either a wet etch or a dry etch.
Wet etching is carried out using a chemical etchant which is highly selective for the particular solid substrate being etched. A major problem with wet etching is that an undercut often times develops on each edge of the photoresist. This property of undercutting the photoresist makes it impossible to achieve sub-tenth micrometer geometry reproducibly. Moreover, in order to etch a pattern into a solid substrate having multiple depths, repeated wet etching steps are required.
In the case of dry etching, ion beam etching (IBE) and reactive ion etching (RIE) are known in the art. These dry etching techniques are both line-of-sight etching processes and are able to produce higher resolution patterns with tighter dimensional control. Despite this, each of these dry etching techniques suffer from unique problems.
A major problem associated with IBE is that the edges of all features of the photoresist are etched at a faster rate due to a high flux of incident ions. This phenomenon is caused by the reflection of bombarding ions off the side walls of the photoresist. The above property associated with IBE is referred to in the art as "trenching" and it typically causes roughening at the edges of the etched features.
The problem generally encountered using RIE is the formation of tall, narrow pedestals of unetched material at the bottom of the pattern feature. This phenomenon which is referred to in the art as "grassing" is caused by localized masking of the photoresist during RIE. Such pedestals may be removed by utilizing a wet etch process.
In view of the drawbacks mentioned hereinabove, prior art etching processes (dry and wet etching alike) are incapable of providing geometrically controlled removal of material from a solid substrate. Moreover, multiple etching steps are generally required to produce a pattern in a solid substrate that has varying depths. Additionally, many complex geometries, such as curved or angled surfaces, are difficult or even impossible to create using existing prior art methods. Thus, there remains a need for developing a method for providing geometrically controlled removal of material from a solid substrate whereby patterning of the solid substrate is achieved without using prior art photolithographic processes. Moreover, there is also a need for developing a method wherein a pattern having different depths is produced in a solid substrate utilizing a single step replacing the multiple photolithographic steps required by the prior art to obtain the same pattern.